To assess the influence of abnormalities found on physical examination of the hips and knees on disability 1156 men and 1739 women aged > or = 55 yr (the Rotterdam Study) were asked about locomotor disability (LD) using six questions of the Health Assessment Questionnaire (HAQ). The prevalence of LD was 20.2% for men and 31.9% for women. Moderately restricted range of motion of the hips and knees occurred in 34.5% of the men and 38.6% of the women. The prevalence of instability of the knees was 12.5% for men and 16.8% for women. Varus deformity in men (10.1%) and valgus deformity in women (15.0%) were the most common deformities of the knees. Restricted flexion of the hips was the strongest determinant of LD. Age-adjusted odds ratios for restricted hip flexion of LD were 4.7% (95% CI: 3.2-6.8) for men and 3.5 (2.7-4.5) for women. Valgus deformity, knee instability and obliquity were risk factors only in women. Adjustment of these odds ratios for morning stiffness and joint pain did not alter the estimates.